Core-skin fiber comprising propylene ethylene random copolymer

ABSTRACT

A skin-core fiber havinga skin of a propylene ethylene copolymer having:i) xylene soluble fraction from 14 wt % to 27 wt %;ii) intrinsic viscosity of the fraction soluble in xylene at 25° C. from 1.0 to 2.4 dl/g;iii) melt flow rate, MFR, from 12 g/10 min to 60 g/10 min;iv) an ethylene derived units content from 5.0 wt % to 12.0 wt %;v) the ethylene derived units content of the fraction insoluble in xylene from 2.5 wt % to 6.0 wt %;vi) the ethylene derived units content of the fraction soluble in xylene ranging from 15.2. wt % to 30.2 wt %;vii) C13 NMR sequences PEP on the fraction insoluble in xylene from 3.5 mol % to 5.5 mol %; andviii) C13 NMR sequences PEP on the fraction soluble in xylene from 11.0 mol % to 14.2 mol %; anda core of a polyethylene having a density between 0.940 g/cm3 to 0.975 g/cm3.

FIELD OF THE INVENTION

In general, the present disclosure relates to the field of chemistry.More specifically, the present disclosure relates to polymer chemistry.In particular, the present disclosure relates to fibers made from orcontaining a propylene ethylene random copolymer.

BACKGROUND OF THE INVENTION

In some embodiments, nonwoven webs or fabrics are used in products suchas workwear, workwear materials, garments, disposable diapers, and otherpersonal hygiene products, including pre-moistened wipes. Disposableabsorbent garments include diapers, incontinence briefs, training pants,and feminine hygiene products. In some instances, nonwoven webs areselected for strength, softness, and abrasion resistance.

SUMMARY OF THE INVENTION

In a general embodiment, the present disclosure provides a skin-corefiber made from or containing

-   -   a skin made from or containing a propylene ethylene copolymer        having:        -   i) a xylene soluble fraction at 25° C. ranging from 14 wt %            to 27 wt %, based upon the total weight of the propylene            ethylene copolymer;        -   ii) an intrinsic viscosity of the fraction soluble in xylene            at 25° C. ranging from 1.0 to 2.4 dl/g;        -   iii) a melt flow rate, MFR, measured according to ISO 1133            at 230° C. with a load of 2.16 kg, ranging from 12 g/10 min            to 60 g/10 min;        -   iv) an ethylene derived units content ranging from 5.0 wt %            to 12.0 wt %, based upon the total weight of the propylene            ethylene copolymer;        -   v) the ethylene derived units content of the fraction            insoluble in xylene at 25° C. ranging from 2.5 wt % to 6.0            wt %;        -   vi) the ethylene derived units content of the fraction            soluble in xylene at 25° C. ranging from 15.2. wt % to 30.2            wt %        -   vii) C¹³ NMR sequences PEP measured on the fraction            insoluble in xylene at 25° C. ranging from 3.5 mol % to 5.5            mol %; and        -   viii) C¹³ NMR sequences PEP measured on the fraction soluble            in xylene at 25° C. ranging from 11.0 mol % to 14.2 mol %;            and    -   a core made from or containing a homopolymer or copolymer of        ethylene having a density between 0.940 g/cm³ to 0.975 g/cm³.

DETAILED DESCRIPTION OF THE INVENTION

In some embodiments, the present disclosure provides a skin-core fibermade from or containing

-   -   a skin made from or containing a propylene ethylene copolymer        having:        -   i) a xylene soluble fraction at 25° C. ranging from 14 wt %            to 27 wt %; alternatively from 17 wt % to 25 wt %;            alternatively from 18 wt % to 22 wt %, based upon the total            weight of the propylene ethylene copolymer;        -   ii) an intrinsic viscosity of the fraction soluble in xylene            at 25° C. ranging from 1.0 to 2.4 dl/g; alternatively from            1.5 to 2.2 dl/g; alternatively from 1.7 to 2.1 dl/g;        -   iii) a melt flow rate, MFR, measured according to ISO 1133            at 230° C. with a load of 2.16 kg, ranging from 12.0 g/10            min to 60.0 g/10 min; alternatively from 15.0 g/10 min to            50.0 g/10 min; alternatively from 18.6 g/10 min to 30.0 g/10            min;        -   iv) an ethylene derived units content ranging from 5.0 wt %            to 12.0 wt %, alternatively from 6.2 wt % to 10.3 wt %,            based upon the total weight of the propylene ethylene            copolymer        -   v) the ethylene derived units content of the fraction            insoluble in xylene at 25° C. ranging from 2.5 wt % to 6.0            wt %; alternatively ranging from 3.2 wt % to 5.2 wt %;            alternatively ranging from 3.5 wt % to 5.0 wt %;        -   vi) the ethylene derived units content of the fraction            soluble in xylene at 25° C. ranging from 15.2. wt % to 30.2            wt %; alternatively ranging from 17.2 wt % to 24.8 wt %;            alternatively ranging from 18.2 wt % to 22.8 wt %;        -   vii) C¹³ NMR sequences PEP measured on the fraction            insoluble in xylene at 25° C. ranging from 3.5 mol % to 5.5            mol %; alternatively ranging from 3.8 mol % to 5.2 mol %;            alternatively ranging from 3.9 mol % to 4.8 mol %; and        -   viii) C¹³ NMR sequences PEP measured on the fraction soluble            in xylene at 25° C. ranging from 11.0 mol % to 14.2 mol %;            alternatively ranging from 11.5 mol % to 13.8 mol %;            alternatively ranging from 12.3 mol % to 13.5 mol %; and    -   a core made from or containing a homopolymer or copolymer of        ethylene having a density between 0.940 g/cm³ to 0.975 g/cm³;        alternatively between 0.955 g/cm³ and 0.970 g/cm³; alternatively        between 0.958 g/cm³ and 0.965 g/cm³.

As used herein, the term “copolymer” refers to polymers containing twokinds of comonomers. In some embodiments, the comonomers are propyleneand ethylene.

In some embodiments and in the propylene ethylene copolymer, the C¹³ NMRsequences PEE measured on the fraction soluble in xylene at 25° C. rangefrom 7.2 mol % to 12.0 mol %; alternatively from 8.3 mol % to 11.2 mol%.

In some embodiments and in the propylene ethylene copolymer, the C¹³ NMRsequences EEE measured on the fraction soluble in xylene at 25° C. arelower than 6.5 mol % alternatively in a range from 5.9 mol % to 2.0 mol%.

In some embodiments and in the propylene ethylene copolymer, the productof reactivity ratio r1r2 of the fraction insoluble in xylene at 25° C.measured with C¹³ NMR is between 2.4 and 4.6; alternatively between 2.9and 4.1; alternatively between 3.1 and 3.8.

Propylene ethylene copolymer is obtained with a process being carriedout in a reactor having two interconnected polymerization zones, a riserand a downcomer, wherein the growing polymer particles:

-   -   (a) flow through the first polymerization zone, the riser, under        fast fluidization conditions in the presence of propylene and of        ethylene;    -   (b) leave the riser and enter the second polymerization zone,        the downcomer, through which the growing polymer particles flow        downward in a densified form in the presence of propylene and        ethylene, wherein the concentration of ethylene in the downcomer        is higher than in the riser; and    -   (c) leave the downcomer and are reintroduced into the riser,        thereby establishing a circulation of polymer between the riser        and the downcomer.

In the first polymerization zone (riser), fast fluidization conditionsare established by feeding a gas mixture made from or containing one ormore alpha-olefins at a velocity higher than the transport velocity ofthe polymer particles. In some embodiments, the velocity of the gasmixture is between 0.5 and 15 m/s, alternatively between 0.8 and 5 m/s.As used herein, the terms “transport velocity” and “fast fluidizationconditions” are as defined in “D. Geldart, Gas Fluidisation Technology,page 155 et seq., J. Wiley & Sons Ltd., 1986”.

In the second polymerization zone (downcomer), the polymer particlesflow under the action of gravity in a densified form, thereby achievingthe high values of density of the solid (mass of polymer per volume ofreactor) and approaching the bulk density of the polymer. As usedherein, the term “densified form” of the polymer indicates that theratio between the mass of polymer particles and the reactor volume ishigher than 80% of the “poured bulk density” of the polymer. In thedowncomer, the polymer flows downward in a plug flow and smallquantities of gas are entrained with the polymer particles.

In some embodiments, the two interconnected polymerization zones areoperated such that the gas mixture coming from the riser is totally orpartially prevented from entering the downcomer by introducing into theupper part of the downcomer a liquid or gas stream, denominated “barrierstream”, having a composition different from the gaseous mixture presentin the riser. In some embodiments, one or more feeding lines for thebarrier stream are placed in the downcomer close to the upper limit ofthe volume occupied by the polymer particles flowing downward in adensified form.

In some embodiments, this liquid/gas mixture fed into the upper part ofthe downcomer partially replaces the gas mixture entrained with thepolymer particles entering the downcomer. The partial evaporation of theliquid in the barrier stream generates in the upper part of thedowncomer a flow of gas, which moves counter-currently to the flow ofdescending polymer, thereby acting as a barrier to the gas mixturecoming from the riser and entrained among the polymer particles. In someembodiments, the liquid/gas barrier fed to the upper part of thedowncomer is sprinkled over the surface of the polymer particles. Insome embodiments, the evaporation of the liquid provides the upward flowof gas.

In some embodiments, the feed of the barrier stream causes a differencein the concentrations of monomers or hydrogen (molecular weightregulator) inside the riser and the downcomer, thereby producing abimodal polymer.

In some embodiments, the gas-phase polymerization process involves areaction mixture made from or containing the gaseous monomers, inertpolymerization diluents and chain transfer agents to regulate themolecular weight of the polymeric chains. In some embodiments, hydrogenis used to regulate the molecular weight. In some embodiments, thepolymerization diluents are selected from C₂-C₈ alkanes, alternativelyfrom the group consisting of propane, isobutane, isopentane and hexane.In some embodiments, propane is used as the polymerization diluent inthe gas-phase polymerization.

In some embodiments, the barrier steam is made from or containing:

-   -   i. from 10 to 100% by mol of propylene, based upon the total        moles in the barrier stream;    -   ii. from 0 to 80% by mol of ethylene, based upon the total moles        in the barrier stream;    -   iii. from 0 to 30% by mol of propane, based upon the total moles        in the barrier stream;    -   iv. from 0 to 5% by mol of hydrogen, based upon the total moles        in the barrier stream.

In some embodiments, the composition of the barrier stream is obtainedfrom the condensation of a part of the fresh monomers and propane,wherein the condensed part is fed to the upper part of the downcomer ina liquid form. In some embodiments, the composition of the barrierstream is derived from condensation or distillation of part of a gaseousstream continuously recycled to the reactor having two interconnectedpolymerization zones.

In some embodiments, additional liquid or gas is fed along the downcomerat a point below the barrier stream.

In some embodiments, the recycle gas stream is withdrawn from agas/solid separator placed downstream the riser, cooled by passagethrough an external heat exchanger and then recycled to the bottom ofthe riser. In some embodiments, the recycle gas stream is made from orcontaining the gaseous monomers, the inert polymerization components,and chain transfer agents. In some embodiments, the inert polymerizationcomponents include propane. In some embodiments, the chain transferagents include hydrogen. In some embodiments, the composition of thebarrier stream deriving from condensation or distillation of the gasrecycle stream is adjusted by feeding liquid make-up monomers andpropane before the gas recycle stream's introduction into the upper partof downcomer.

In some embodiments and in both riser and downcomer, the temperature isbetween 60° C. and 120° C., while the pressure ranges from 5 to 40 bar.

In some embodiments, the process for preparing the propylene ethylenecopolymer is carried out in presence of a highly stereospecificheterogeneous Ziegler-Natta catalyst. In some embodiments, theZiegler-Natta catalysts are made from or containing a solid catalystcomponent made from or containing at least one titanium compound havingat least one titanium-halogen bond and at least an electron-donorcompound (internal donor), both supported on magnesium chloride. In someembodiments, the Ziegler-Natta catalysts systems are further made fromor containing an organo-aluminum compound as a co-catalyst andoptionally an external electron-donor compound.

In some embodiments, the catalysts systems are as described in theEuropean Patent Nos. EP45977, EP361494, EP728769, and EP 1272533 andPatent Cooperation Treaty Publication No. W000163261.

In some embodiments, the organo-aluminum compound is an alkyl-Alselected from the trialkyl aluminum compounds. In some embodiments, thetrialkyl aluminum compound is selected from the group consisting oftriethylaluminum, triisobutylaluminum, tri-n-butylaluminum,tri-n-hexylaluminum, and tri-n-octylaluminum. In some embodiments, thetrialkylaluminum is mixed with alkylaluminum halides, alkylaluminumhydrides or alkylaluminum sesquichlorides such as AlEt₂Cl and Al₂Et₃Cl₃.

In some embodiments, the external electron-donor compounds are selectedfrom the group consisting of silicon compounds, ethers, esters, amines,heterocyclic compounds, ketones and 1,3-diethers. In some embodiments,the ester is ethyl 4-ethoxybenzoate. In some embodiments, the externalelectron-donor compound is 2,2,6,6-tetramethyl piperidine. In someembodiments, the external donor compounds are silicon compounds offormula R_(a) ⁵R_(b) ⁶Si(OR⁷)_(c) where a and b are integer from 0 to 2,c is an integer from 1 to 3 and the sum (a+b+c) is 4; R⁵, R⁶, and R⁷,are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionallycontaining heteroatoms. In some embodiments, the silicon compounds areselected from the group consisting of methylcyclohexyldimethoxysilane,diphenyldimethoxysilane, methyl-t-butyldimethoxysilane,dicyclopentyldimethoxysilane,2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1,trifluoropropyl-2-ethylpiperidinyl-dimethoxysilane and 1,1,1,trifluoropropyl-methyldimethoxysilane. In some embodiments, the externalelectron donor compound is used in an amount to give a molar ratiobetween the organo-aluminum compound and the electron donor compound offrom 0.1 to 500; alternatively from 1 to 100; alternatively from 2 to50.

In some embodiments, the propylene ethylene copolymer compositions arefurther made from or containing additives and/or peroxides, therebyachieving a certain Melt Flow Rate.

In some embodiments, the additives are selected from the groupconsisting of pigments, opacifiers, fillers, stabilizers, flameretardants, antacids and whiteners.

As used herein, the phrase “fibers or filaments having a skin-corestructure” refers to fibers or filaments having an axially extendinginterface and made from or containing at least two components, that is,at least an inner core and at least an outer skin, wherein the at leasttwo components are made from or containing different polymeric materialsand are joined along the axially extending interface. In someembodiments and in skin-core fibers or filaments, the skin thickness isuniform or is not uniform around the circumference of the fiber orfilament cross-section.

In some embodiments, fibers or filaments having skin-core structure areproduced using melt-spin equipment having eccentric or concentricannular dies.

In some embodiments, the skin-core fibers or filaments are made from orcontaining 50-80% by weight, alternatively 55-75% by weight, ofpolymeric material forming the core-layer and 20-50% by weight,alternatively 25-45% by weight, of polymer material forming the outerskin-layer, with respect to the total weight of the fibers or filaments.

In some embodiments, the fibers have a diameter of 10 to 50 micrometers.

In some embodiments, the fibers are spread to form directly a fiber weband calendered, thereby obtaining a non-woven fabric.

In some embodiments and in a spunbonding process, the polymer is heatedin an extruder to the melting point of the polyolefin composition andthen the molten polyolefin composition is pumped under pressure througha spinneret containing a number of orifices of certain diameter, therebyproducing filaments of the molten polymer composition and withoutsubjecting the filaments to a subsequent drawing.

In some embodiments, the equipment includes an extruder with a die onthe extruder's spinning head, a cooling tower, and an air suctiongathering device that uses Venturi tubes.

In some embodiments, the filaments are gathered over a conveyor belt,where the filaments are distributed and thereby forming a web.

In some embodiments, the spunbond machinery is used under the followingprocess conditions:

-   -   the output per hole ranges from 0.3-0.8 g/min, alternatively        from 0.4-0.6 g/min;    -   the molten polymer filaments fed from the face of the spinneret        are cooled by air flow and solidified as a result of cooling;        and    -   the spinning temperature is between 2000 and 300° C.

The filaments are brought by the conveyor belt to a thermal bondingstep, which is carried out by calendering through a couple of heatedrolls.

In some embodiments, the thermal bonding temperatures range from 120° C.to 170° C.

In some embodiments, the fabric is made from or containing monolayer ormultilayer non-woven fabrics.

In some embodiments, the non-woven fabric is multilayered and at leastone layer is made from or containing fibers formed from the propyleneethylene copolymer. In some embodiments, the other layer is obtained byspinning processes other than spunbond. In some embodiments, the otherlayer is made from or containing other types of polymers.

In some embodiments, the tenacity in the transverse direction direction(TD) of the non-woven fabric ranges from 12.0 to 24.0 N, alternativelyfrom 12.5 to 20 N.

In some embodiments, haptics range from 12 to 18.

The following examples are given to illustrate, not to limit, thepresent disclosure:

EXAMPLES

Xylene-Soluble (XS) Fraction at 25° C.

Xylene Solubles at 25° C. was determined according to ISO 16 152; withsolution volume of 250 ml, precipitation at 25° C. for 20 minutes,including 10 minutes with the solution in agitation (magnetic stirrer),and drying at 70° C.

DSC Method for Melting Point

Melting point was measured according to ISO 11357-3, at scanning rate of20 C/min both in cooling and heating, on a sample of weight between 5and 7 mg, under inert N2 flow. The instrument was calibrated withindium.

Glass Transition Temperature Via DMTA (Dynamic Mechanical ThermalAnalysis)

Molded specimens of 76 mm by 13 mm by 1 mm were fixed to a DMTA machinefor tensile stress. The frequency of the tension and relies of thesample were fixed at 1 Hz. The DMTA translates the elastic response ofthe specimen starting from −100° C. to 130° C. The elastic response wasplotted versus temperature. The elastic modulus for a viscoelasticmaterial is defined as E=E′+iE″. The DMTA split the two components E′and E″ by resonance, plotted E′ vs temperature, and plotted E′/E″=tan(δ) vs temperature. The glass transition temperature Tg was assumed tobe the temperature at the maximum of the curve E′/E″=tan (δ) vstemperature.

Density

The density of samples was measured according to ISO 1183-1:2012 at 23°C. (ISO 1183-1 method A “Methods for determining the density ofnon-cellular plastics Part 1: Immersion method, liquid pyknometer methodand titration method”; Method A: Immersion method, for solid plastics(except for powders) in void-free form). Test specimens were taken fromcompression molded plaques conditioned for 10 days before carrying outthe density measure.

Melt Flow Rate (MFR)

Measured according to ISO 1133 at 230° C. with a load of 2.16 kg, unlessotherwise specified.

Intrinsic Viscosity (IV)

The sample was dissolved in tetrahydronaphthalene at 135° C. and thenpoured into a capillary viscometer. The viscometer tube (Ubbelohde type)was surrounded by a cylindrical glass jacket, which permittedtemperature control with a circulating thermostatic liquid. The downwardpassage of the meniscus was timed by a photoelectric device.

The passage of the meniscus in front of the upper lamp started thecounter, which had a quartz crystal oscillator. The counter stopped asthe meniscus passed the lower lamp, and the efflux time was registered.The efflux time was converted into a value of intrinsic viscositythrough Huggins' equation (Huggins, M. L., J. Am. Chem. Soc., 1942, 64,2716) based upon the flow time of the solvent at the same experimentalconditions (same viscometer and same temperature). A single polymersolution was used to determine [η].

Ethylene Content in the Copolymers

¹³C NMR spectra were acquired on a Bruker AV-600 spectrometer equippedwith cryoprobe, operating at 160.91 MHz in the Fourier transform mode at120° C.

The peak of the Sββ carbon (nomenclature according to “Monomer SequenceDistribution in Ethylene-Propylene Rubber Measured by ¹³C NMR. 3. Use ofReaction Probability Mode” C. J. Carman, R. A. Harrington and C. E.Wilkes, Macromolecules, 1977, 10, 536) was used as an internal referenceat 29.9 ppm. The samples were dissolved in 1,1,2,2-tetrachloroethane-d2at 120° C. with an 8% wt/v concentration. Each spectrum was acquiredwith a 900 pulse, and 15 seconds of delay between pulses and CPD toremove ¹H-¹³C coupling. 512 transients were stored in 32K data pointsusing a spectral window of 9000 Hz.

The assignments of the spectra, the evaluation of triad distribution andthe composition were made according to Kakugo (“Carbon-13 NMRdetermination of monomer sequence distribution in ethylene-propylenecopolymers prepared with δ-titanium trichloride-diethyl-aluminumchloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake,Macromolecules, 1982, 15, 1150) using the following equations:

PPP = 100  T ββ/S PPE = 100  T βδ/S EPE = 100  T δδ/S PEP = 100  S ββ/SPEE = 100  S β δ/S EEE = 100  (0.25  S γδ + 0.5  S δδ)/SS = T ββ + T βδ + T δδ + S ββ + S βδ + 0.25  S γδ + 0.5  S δδ

The molar percentage of ethylene content was evaluated using thefollowing equation:

${r_{1}r_{2}} = {1 + \left( {\frac{{EEE} + {PEE}}{PEP} + 1} \right) - {\left( {\frac{P}{E} + 1} \right)\left( {\frac{{EEE} + {PEE}}{PEP} + 1} \right)^{0.5}}}$The weight percentage of ethylene content was evaluated using thefollowing equation:

$W = \frac{12 \cdot \left\lbrack {\sum_{j = 1}^{n}\left( {R_{j} - \overset{\_}{R}} \right)^{2}} \right\rbrack}{r^{2}{n\left( {n - 1} \right)}\left( {n + 1} \right)}$where P % mol is the molar percentage of propylene content, while MWEand MWP are the molecular weights of ethylene and propylene,respectively.

The product of reactivity ratio r1r2 was calculated according to Carman(C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977;10, 536) as:

The tacticity of Propylene sequences was calculated as mm content fromthe ratio of the PPP mmT_(ββ) (28.90-29.65 ppm) and the whole T_(ββ)(29.80-28.37 ppm).

Tenacity and Elongation at Break of Non-Woven Fabrics

Test pieces 50 mm large and

E %  mol = 100 * [PEP + PEE + EEE]about 100 mm long were obtained by cutting the non-woven fabrics, withthe longer side in the Machine Direction (MD), corresponding to thedirection of movement of the spun-bond conveyor belt, or in theTransverse Direction (TD), perpendicular to the Machine direction. Thetwo opposite 50 mm sides of the sample were fixed to the clamps of anInstron dynamometer (model 1122) and tensioned to break with a crossheadspeed of 100 mm/min, the initial distance between the clamps being of100 mm. The ultimate strength (load at break) and the elongation atbreak were determined.

Both tenacity and elongation were measured in TD, using the respectivelycut test pieces.

Example 1

Preparation of the Ziegler-Natta Solid Catalyst Component

The Ziegler-Natta catalyst was prepared as described for Example 5,lines 48-55, of European Patent No. EP728769B1.

Preparation of the Catalyst System—Precontact

Before introducing the solid catalyst component into the polymerizationreactors, the solid catalyst component was contacted withaluminum-triethyl (TEAL) and dicyclopentyldimethoxysilane (D donor)under the conditions reported in Table 1.

Prepolymerization

The catalyst system was then subjected to prepolymerization treatment at20° C. by maintaining the catalyst system in suspension in liquidpropylene for a residence time of 9 minutes before introducing thecatalyst system into the polymerization reactor.

Polymerization

The polymerization was carried out in gas-phase polymerization reactorincluding two interconnected polymerization zones, a riser and adowncomer, as described in European Patent No. EP782587. Hydrogen wasused as a molecular weight regulator. The polymer particles exiting fromthe polymerization step were subjected to a steam treatment to removethe unreacted monomers and dried under a nitrogen flow.

The main precontact, prepolymerization and polymerization conditions andthe quantities of monomers and hydrogen fed to the polymerizationreactor are reported in Table 1.

TABLE 1 Example 1 PRECONTACT Temperature ° C. 15 Residence Time min 13TEAL/catalyst wt/wt 8 TEAL/Ext. Donor g/g 4 PREPOLYMERIZATIONTemperature ° C. 20 Residence Time min 8 POLYMERIZATION Temperaturebar-g 65 Pressure bar-g 24 Residence Time min 111 Split holdup riser wt% 40 Split holdup downcomer wt % 60 C₂ ⁻/C₂ ⁻ + C3⁻ riser mol/mol 0.012C₂ ⁻/C₂ ⁻ + C3⁻ downcomer mol/mol 0.032 H₂/C₃ ⁻ riser mol/mol 0.026H₂/C₂ ⁻ downcomer mol/mol 0.186 H₂ = hydrogen; C²⁻ = ethylene, C³⁻ =propylene

The resulting polymer had an MFR of 2.11 g/10 min and was visbroken toMFR 27.8 g/10 min. Properties of the visbroken polymer are reported inTable 2.

TABLE 2 Ex 1 Ethylene content Wt % 7.6 Xylene soluble at 25° C. Wt %17.5 Intrinsic viscosity xylene dl/g 1.56 solubles MFR g/10 27.8 minEthylene in the fraction Wt % 4.35 insoluble in xylene at 25° C.Ethylene in the fraction Wt % 24.40 soluble in xylene at 25° C. PEPsequences in the fraction Mol % 3.94 insoluble in xylene at 25° C. PEPsequences in the fraction Mol % 12.25 soluble in xylene at 25° C. PEEsequences in the fraction Mol % 12.89 soluble in xylene at 25° C. EEEsequences in the fraction Mol % 8.98 soluble in xylene at 25° C. r₁r₂ inthe fraction insoluble in 4.83 xylene at 25° C. Melting point ° C. 142.4

Production of Non-Woven Fabric Example 2 and Comparative Example 3.

Non-woven fabrics made of concentric skin-core composite filaments wereprepared.

In Example 2, the skin was made of the polymer of Example 1 and the corewas made from Hostalen GX5052 high density polyethylene, which wascommercially available from LyondellBasell and having a density of 0.963g/cm3. In Example 3, the skin was made with the polymer of Example 1 andthe core was made with Moplen HP561R homopolymer, which was commerciallyavailable from LyondellBasell. In Comparative Example 4, the skin wasmade with Hostalen GX5052 high density polyethylene (which wascommercially available from LyondellBasell) and the core was made withMoplen HP561R homopolymer (which was commercially available fromLyondellBasell).

The polymer materials, were fed to a Reicofil 4 spunbond pilot line,which was run with the following settings and operative conditions:

-   -   core/skin 70/30 (whole diameter: 0.6 mm);    -   line speed (m/min): 214 (17 gsm*)-73 (50 gsm);    -   spinneret: 7377 holes (6827 holes/m);    -   gap pre-diffusor (exit): 23 mm;    -   Secondary air gap—right/left: 14 mm;    -   gap diffusor exit: 75 mm; and    -   distance above the belt right/left: 131 mm.    -   gsm=grams per square meter.

The thermal bonding was carried out with the hot rolls at thetemperatures reported in Table 3.

The non-woven fabrics were made of composite filaments with concentriccore and skin structure in a weight ratio of 70% of core and 30% ofskin.

The mechanical properties of the non-woven fabrics are reported in Table3.

TABLE 3 Example Ex. 2 Comp Ex. 3 Skin Ex 1 GX5052 Core GX5052 HP561RThermal bonding [° C.] 123 123 temperature Non-woven properties haptics14.5 10.0 Note: TD = Transverse Direction

Haptics has been Measured with the Following Method:

Textile specimens were assessed by a panel of 25 evaluators. Textilematerials in foils with dimensions of 40 cm×40 cm were used. Thespecimens were identified with a code (anonymous), which did not reflectthe name of the parent material. Each specimen was used for oneevaluation for each member of the panel.

Two fabric extremes for the characteristic of interest were chosen and,to such specimen extremes, arbitrary numerical values were assigned (ascale from 0 to 10). Specimens to be evaluated were then assigned valueswithin the established numerical scale, according to the differencesfelt.

Kendall coefficient of concordance W was used to check if theconcordance among the evaluators were acceptable, using the followingformula

100 * E%  mol * MWE E%  wt. = E %  mol * MWE + P%  mol * MWP

where R_(j) was the sum of ranks given to each fabric sample; R was themean value of rank sum; r is the number of evaluators and n is thenumber of specimens. When the value of W is greater of 0.61, theconcordance among the evaluators was considered acceptable.

The features evaluated were the following:

Subjective assessment Characteristic Definition techniqueHardness/Softness Resistance of Compress the sample compression with thehands.An average of the evaluations was calculated.

What is claimed is:
 1. A skin-core fiber comprising: a skin comprising apropylene ethylene copolymer having i) a xylene soluble fraction at 25°C. ranging from 14 wt % to 27 wt %, based upon the total weight of thepropylene ethylene copolymer; ii) an intrinsic viscosity of the fractionsoluble in xylene at 25° C. ranging from 1.0 to 2.4 dl/g; iii) a meltflow rate, MFR, measured according to ISO 1133 at 230° C. with a load of2.16 kg, ranging from 12 g/10 min to 60.0 g/10 min; iv) an ethylenederived units content ranging from 5.0 wt % to 12.0 wt %, based upon thetotal weight of the propylene ethylene copolymer; v) the ethylenederived units content of the fraction insoluble in xylene at 25° C.ranging from 2.5 wt % to 6.0 wt %; vi) the ethylene derived unitscontent of the fraction soluble in xylene at 25° C. ranging from 15.2.wt % to 30.2 wt %; vii) C¹³ NMR sequences PEP measured on the fractioninsoluble in xylene at 25° C. ranging from 3.5 mol % to 5.5 mol %; andviii) C¹³ NMR sequences PEP measured on the fraction soluble in xyleneat 25° C. ranging from 11.0 mol % to 14.2 mol %; and a core comprising ahomopolymer or copolymer of ethylene having a density between 0.940g/cm³ to 0.975 g/cm³.
 2. The skin-core fiber according to claim 1,wherein the polymeric material forming the core-layer ranges from 50 to80 wt % and the polymeric material forming the outer skin-layer rangesfrom 20 wt % to 50 wt %.
 3. The skin-core fiber according to claim 1,wherein, in the propylene ethylene copolymer, the xylene solublefraction at 25° C. ranges from 17 wt % to 25 wt %.
 4. The skin-corefiber according to claim 1, wherein, in the propylene ethylenecopolymer, the intrinsic viscosity of the fraction soluble in xylene at25° C. ranges from 1.5 to 2.2 dl/g.
 5. The skin-core fiber according toclaim 1, wherein, in the propylene ethylene copolymer, the melt flowrate, MFR, measured according to ISO 1133 at 230° C. with a load of 2.16kg, ranges from 15.0 g/10 min to 50.0 g/10 min.
 6. The skin-core fiberaccording to claim 1, wherein, in the propylene ethylene copolymer, theC¹³ NMR sequences PEP measured on the fraction insoluble in xylene at25° C. ranges from 3.8 mol % to 5.2 mol %; and the C¹³ NMR sequences PEPmeasured on the fraction soluble in xylene at 25° C. ranges from 11.5mol % to 13.8 mol.
 7. The skin-core fiber according to claim 1, wherein,in the propylene ethylene copolymer, the C¹³ NMR sequences PEP measuredon the fraction insoluble in xylene at 25° C. ranges 3.9 mol % to 4.8mol %; and the C¹³ NMR sequences PEP measured on the fraction soluble inxylene at 25° C. ranges 12.3 mol % to 13.5 mol %.
 8. The skin-core fiberaccording to claim 1, wherein, in the propylene ethylene copolymer, theethylene derived units content of the fraction insoluble in xylene at25° C. ranges from 3.2 wt % to 5.2 wt %.
 9. The skin-core fiberaccording to claim 1, wherein, in the propylene ethylene copolymer, theethylene derived units content of the fraction soluble in xylene at 25°C. ranges from 17.2 wt % to 24.8 wt %.
 10. The skin-core fiber accordingto claim 1, wherein, in the propylene ethylene copolymer, the C¹³ NMRsequences PEE measured on the fraction soluble in xylene at 25° C. rangefrom 7.2 mol % to 12.0 mol %.
 11. The skin-core fiber according to claim1, wherein, in the propylene ethylene copolymer, the C¹³ NMR sequencesEEE measured on the fraction soluble in xylene at 25° C. are lower than6.5 mol %.
 12. The skin-core fiber according to claim 1, wherein, in thepropylene ethylene copolymer, the product of reactivity ratio r1r2 ofthe fraction insoluble in xylene at 25° C. measured with C¹³ NMR isbetween 2.4 and 4.6.
 13. The skin-core fiber according to claim 1,wherein the core layer comprises a homopolymer or copolymer of ethylenehaving a density comprised between 0.955 g/cm³ and 0.970 g/cm³.
 14. Theskin-core fiber according to claim 1, wherein the core layer comprises ahomopolymer or copolymer of ethylene having a density between 0.958g/cm³ and 0.965 g/cm³.
 15. A non-woven fabric comprising the skin-corefiber according to claim 1.